Regulation EC 245/2009 (amended by regulation 347/2010) prohibits a number of fluorescent lamps having rare-earth-free phosphor coating. Lamps having the same power consumption but significantly higher luminous efficiency and higher luminous flux have been used as a replacement product, with a coating composed of rare earth phosphors being used. The proportion of rare earths is disadvantageous here since rare earths are increasingly running short and their prices on the world market have increased greatly in recent years. Therefore, there is a need for fluorescent lamps having a reduced proportion of rare earths and having the same efficiency and the same luminous flux stability as the fluorescent lamps currently in use, in order thus to reduce the material costs and to reduce environmental burdens resulting from the extraction and transport of rare earths.
In order to reduce the proportion of rare earths, fluorescent lamps have previously been produced in a double-layer design, wherein the lower layer consists of a customary halophosphate phosphor and the top layer consists of a mixture containing rare earth phosphors. Disadvantages of these fluorescent lamps include the high loss of light and the higher Hg consumption over the operating life. The loss of light is caused by radiation damage, in particular hard UV radiation e.g. in the VUV range, of the halophosphate phosphor. The higher Hg consumption can be attributed to the fact that Hg diffuses into the halophosphate phosphor grains.
Another measure for reducing the proportion of rare earths is to produce fluorescent lamps in a reflector layer design. In this case, the inner side of the discharge vessel is coated with an Al2O3 protective layer and a top layer containing rare earth phosphors is applied thereabove. Disadvantages in this case include the higher proportion of rare earth phosphors compared with the double-layer design and less covering of the ends of the lamp bulbs as a consequence of layer thickness fluctuations over the lamp bulb length.